This invention relates to the nuclear reactor art and has particular relationship to light-weight power plants for mobile or vehicular propulsion applications where a nuclear reactor is a primary source of energy. Such power plants are shown in Thompson-Pierce U.S. Pat. No. 4,057,465 and Thompson-Spurrier-Jones U.S. Pat. No. 4,088,535. The nuclear reactor included in such power plants is typically gas cooled. Usually the cooling gas is helium.
An important consideration in dealing with nuclear propulsion plants is reliable shutdown of the reactor by control of its reactivity under normal and abnormal conditions. Adequate reliable reactivity control is available for normal shutdown. But a different problem is presented on the occurrence of an emergency which results in failure that affects the reactor so that normal reactivity control is insufficient. This invention concerns itself with the need for reliable shutdown under such emergency conditions. It is an object of this invention to compensate for the insufficiency of the control and thereby provide for reliable shutdown of the reactor thereby precluding the happening of a catastrophe during the emergency.
Typically an emergency can arise when water penetrates into the core of nuclear reactors of certain types. For example a ship propelled by a light-weight power plant including an epithermal-neutron, gas cooled, nuclear reactor is sunk. The penetration of water into the core of the reactor is possible because the ship may sink to a depth, for example exceeding 600 feet, at which the containment of the reactor may rupture or for other reasons. The water may materially increase the nuclear reactivity of the reactor and thus may lead to a nuclear excursion and a serious catastrophe. it is an object of this invention to effectively and permanently deactivate the nuclear reactor supplying the primary energy to the propulsion plant of a ship when the ship is sunk and to accomplish this purpose before water can flood the core of the reactor.